Samples taken from the vultures' facial skin showed a massive variety of 528 different types of micro-organisms. But only 76 survived in the gut.

"Our results show that there has been strong (evolutionary) adaptation in vultures when it comes to dealing with the toxic bacteria they digest," said Michael Roggenbuck of the University of Copenhagen.

"On the one hand, vultures have developed an extremely tough digestive system, which simply acts to destroy the majority of the dangerous bacteria they ingest.

"On the other hand, vultures also appear to have developed a tolerance towards some of the deadly bacteria -- species that would kill other animals actively seem to flourish in the vulture lower intestines."